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Originally Posted by BrianG
Let's start by saying that motor efficiency has very little to do with ESC heat. The only motor spec that might effect ESC efficiency is the inductance value due to the phase angles produced, which can be more difficult to drive.
Assuming an FET goes rail to rail, the only time an FET dissipates power is when there is a voltage drop across the device AND current flow. If the output of the ESC were perfect square waves (0 rise time), then the ESC would be 100% efficient no matter what the motor is doing with that power. At the 0 point of the square wave, there is full voltage across the FET but 0A (0 watts). At the max point of the square wave, there is 0v dropped but there is max current (0 watts). But during the ramp up (the total time it takes to do this is the slew rate), there is voltage dropped AND current flow, which creates the heat. The longer the ramp, the more power loss and more heat. Higher frequencies have more pulses per second and therefore more "ramp up and downs" which can make them an ESC heat up more. However, too low of a switching frequency will cause the motor to not act correctly.
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Yah, i agree! Power switching is a HUGE issue today!
Check out
THIS , I don't really know how they do this, but they use 24khz switching. Something called 'Softswing", the switching is inaudible (first for EV inverters), and by far the most efficient EV inverter too, with 97% eff.
Also, (check my signature) they told to wait for their new 'Hybrid Synchronous Motor" to come out for my vehicle. Would you have any idea what it would be? They told me it would have very broad eff. range, and good torque range, just a very good motor all around...?
But yah, the internal resistance is only part of the losses of heat, a small part.